librosa does not normalize wave file between [-1, 1]

Question

In passing a file via the use:

librosa_audio, librosa_sample_rate = librosa.load(filename)

The output produces an audio file such that:

Librosa audio file min~max range: -1.2105224 to 1.2942806

The file that I am working on was obtained from https://www.boomlibrary.com/ and had a bit depth of 24. I down sampled to 16 and also up sampled to 32 to work with librosa. Both of these files produced the same min-max range after going through librosa.

Why does this happen?
Is there a way to parse the wav file to Librosa such that the data will fall between [-1,1]?

Here is a link to the files:

https://drive.google.com/drive/folders/12a0ii5i0ugyvdMMRX4MPfWMSN0arD0bn?usp=sharing

Answer 1

The behaviour you are observing stems directly from resampling to 22050 Hz that librosa load does by default:

librosa.core.load(path, sr=22050)

Resampling process always affects the audio, hence you see values that are not normalized. You have to do this yourself.

More likely, you wanted to read the audio with the native sampling rate, in which case you should have passed None to sr like this:

librosa.core.load(path, sr=None)

Example based on the audio sample you have provided:

In [4]: y, sr = librosa.load('201-AWCKARAK47Close0116BIT.wav', sr=None)
In [5]: y.max()
Out[5]: 0.9773865

In [6]: y.min()
Out[6]: -0.8358917